SELECT * FROM
(
SELECT Customer.Customer_ID,Customer.First_Name,Customer.Last_Name,Commercial.Company_Name,Product_Catagory.Product_Catagory_Description, COUNT(Product_Catagory.Product_Catagory_ID) AS Product_Catagory_Count
FROM Customer
INNER JOIN Commercial
ON Commercial.Customer_ID = Customer.Customer_ID
INNER JOIN Order_Table
ON Order_Table.Customer_ID = Customer.Customer_ID
INNER JOIN Order_Item
ON Order_Item.Order_ID = Order_Table.Order_ID
INNER JOIN Product
ON Order_Item.Product_ID = Product.Product_ID
INNER JOIN Product_Catagory_Link
ON Product.Product_ID = Product_Catagory_Link.Product_ID
INNER JOIN Product_Catagory
ON Product_Catagory_Link.Product_Catagory_ID = Product_Catagory.Product_Catagory_ID
GROUP BY Customer.First_Name, Customer.Last_Name, Customer.Customer_ID, Commercial.Company_Name, Product_Catagory.Product_Catagory_Description
ORDER BY Product_Catagory_Count DESC
)
WHERE Customer_ID = 5 AND ROWNUM = 1;